1. Field of the Invention
This invention relates to electronic circuits, and in particular to metal-oxide-semiconductor (herein "MOS") circuits used for comparing the relative magnitude of two independently varying voltages.
2. Prior Art
Electronic circuits for measuring or comparing voltages are known in the art. Most such prior art circuits, however, suffer from the disadvantage of being unnecessarily complex, or difficult to fabricate in integrated circuit embodiments. Devices are also known for turning on a secondary power supply in case of failure of a primary power supply, however, such prior art devices have typically been either mechanical switches or relays, or complicated electronic circuits. Many such prior art devices and structures have been difficult or impossible to implement in integrated circuit form.
Further, with the advent of microprocessors and other electronic apparatus such as volatile semiconductor memories, an interruption or loss of power can destroy valuable data and information. This requires repeating the input of such information, if it is still available, a potentially time-consuming and expensive operation.